Off-axis sheet-handling apparatus and technique for transmission-mode measurements

Abstract

An apparatus ( 2 ) and method, for measuring process-induced features in a transparent sheet ( 10 ). The apparatus includes a light source ( 100 ), an imaging device ( 80 ), and a support structure ( 30 ) disposed between the light source and the imaging device. The support structure is configured and arranged to support the transparent sheet so that measurement error induced by the support structure is viewed by the imaging device as extending along or parallel to a first axis ( 46, 54 ) that is oblique to a second axis ( 22, 24 ) along or parallel to which the process-induced features in the transparent sheet extend when viewed by the imaging device.

1. An apparatus, for measuring process-induced features in a transparent sheet, comprising:
 a light source; 
 an imaging device; and 
 a transparent-sheet support structure disposed between the light source and the imaging device, 
 wherein the support structure is configured and arranged to support a transparent sheet so that measurement error induced by the support structure is viewed by the imaging device as extending along or parallel to a first axis that is oblique to a second axis along or parallel to which the process-induced features in the transparent sheet extend when viewed by the imaging device. 
 
     
     
       2. The apparatus of  claim 1 , wherein the process-induced feature comprises stress. 
     
     
       3. The apparatus of  claim 1 , wherein the support structure includes bars extending along axes oblique to the second axis. 
     
     
       4. The apparatus of  claim 3 , wherein the bars include openings, and the support includes a vacuum source in communication with the openings. 
     
     
       5. The apparatus of  claim 3 , wherein spaces are disposed between the bars, wherein the bars include a first width and the spaces include a second width, and further wherein the first width is less than or equal to the second width. 
     
     
       6. The apparatus of  claim 1 , wherein the imaging device includes pixels oriented along a third axis, wherein the support structure includes spaces through which light from the light source may be viewed by the imaging device, the spaces including longitudinal axes parallel to the first axis, and further wherein the third axis is oblique to the longitudinal axes. 
     
     
       7. A method of measuring process-induced features in a transparent sheet, comprising:
 disposing a transparent sheet on a support structure that is disposed between a light source and an imaging device; 
 supporting the transparent sheet so that measurement error induced by the support structure is viewed by the imaging device as extending along or parallel to a first axis that is oblique to a second axis along or parallel to which the process-induced features in the transparent sheet extend when viewed by the imaging device; 
 capturing a first image of a first section of the transparent sheet; 
 moving the transparent sheet and then capturing a second image of the first section of the transparent sheet; and 
 combining the first and second images to form an image of the process-induced features in the first section of the transparent sheet. 
 
     
     
       8. The method of  claim 7 , wherein the first and second images together cover the entire area of the first section of the transparent sheet. 
     
     
       9. The method of  claim 8 , wherein the first section of the transparent sheet encompasses the entire area of the transparent sheet. 
     
     
       10. The method of  claim 7 , further comprising contacting the transparent sheet with a conveyance device during the step of moving, but not during the steps of capturing the first and second images. 
     
     
       11. The method of  claim 7 , further comprising flattening the transparent sheet prior to the steps of capturing the first and second images, and maintaining the transparent sheet in the flattened condition during the steps of capturing the first and second images. 
     
     
       12. The method of  claim 11 , wherein the step of flattening comprises vacuuming the transparent sheet against the support structure. 
     
     
       13. The method of  claim 7 , wherein the step of combining further comprises removing the measurement error induced by the support structure. 
     
     
       14. The method of  claim 7 , wherein the support structure includes bars extending along axes oblique to the second axis, wherein spaces are disposed between the bars, wherein the bars include a first width and the spaces include a second width, and further wherein the first width is less than or equal to the second width. 
     
     
       15. The method of  claim 14 , wherein the imaging device is capable of capturing an image within a viewing area having a third width, the transparent sheet includes a fourth width, and wherein the third width is larger than the fourth width by an amount equal to or greater than the first width. 
     
     
       16. The method of  claim 15 , wherein the support structure includes a fifth width, and the fifth width is larger than the fourth width by an amount equal to or greater than the first width. 
     
     
       17. The method of  claim 14 , wherein the transparent sheet is moved in a transportation direction relative to the support structure, and wherein the axes of the bars form an angle with the transportation direction, the angle ranging from 25 to 65 degrees. 
     
     
       18. The method of  claim 7 , wherein the transparent sheet is moved in a direction parallel or perpendicular to the second axis. 
     
     
       19. The method of  claim 7 , wherein the imaging device includes pixels extending along a third axis, and further wherein the third axis is oblique to the first axis. 
     
     
       20. The method of  claim 7 , wherein the process-induced feature comprises stress.